Cloth-presser mechanism in a sewing machine

ABSTRACT

A cloth-presser mechanism for use in a sewing machine for bar stitching a button hole at an end thereof is disclosed. The mechanism comprises a pair of work clamps adapted to open and close the button hole slit line, a cam plate adapted to shift between two positions to control the opening and closing action of the work clamps, a control member adapted to control the shifting of the cam plate and to move forward in association with a rotary cam driven from the main shaft of the sewing machine and to move rearwardly regardless of the rotary cam, and a spring element operatively combined in the mechanism to accumulate energy which is required to move the work clamps toward each other to close the button hole due tothe forward movement of the control member.

mes atet 1 [111 3,84,%

Nakamura ay 2%, 1975 CLOTH-PRESSER MECHANISM IN A SEWING MACHINE Primary Examiner-H. Hampton Hunter [75] Inventor: Shirozi Nakamura Tokyo, Japan Attorney, Agent, or Fzrm-Wenderoth, Lind & Ponack [73] Assignee: Tokyo Juki Kobyo Kabushiki Kaisha, Tokyo, Japan [57] ABSTRACT A cloth-presser mechanism for use in a sewing ma- [22] Ffled' 1967 chine for bar stitching a button hole at an end thereof [21] Appl. No.: 662,495 is disclosed. The mechanism comprises a pair of work clamps adapted to open and close the button hole slit line, a cam plate adapted to shift between two posi- [30] Forelgn Apphcatlon Prmmy Data tions to control the opening and closing action of the Sept. 10, 1966 Japan 41-59715 Work Clamps, a Control member adapted to control the shifting of the cam plate and to move forward in asso- [52] US. Cl. 112/70 Ciation with a rotary cam driven from the main shaft [51] Int. Cl D05b 3/06 of the sewing machine and to move rearwardly regarch [58] Field of Search 112/70, 65, 66, 73, 74, less of the rotary cam, and a Spring element 0pera 112/76 tively combined in the mechanism to accumulate energy which is required to move the work clamps to- References C'ted ward each other to close the button hole due tothe UNITED STATES PAT forward movement of the control member.

1,247,139 ll/l9l7 Nelson [12/70 1,892,895 1/1933 Kiewicz 112/70 1 Claim, 9 Drawing Figures PATENTEU HAY 2 01975 SHEET 10? 4 PATENTEI] MAY 2 0 I975 SHEET 2 0; 4

PATENTEDHAY20I975 3,884.164

SHEET 30F 4 CLOTH-PRESSER MECHANISM IN A SEWING MACHINE BACKGROUND OF THE INVENTION This invention relates to a cloth-presser (or work clamp) mechanism for use in a sewing machine, and more particularly to a work clamp mechanism operable to cause the cloth-presser or work clamps, which are adapted to hold the cloth or work along a button hole from above the cloth and to close the button hole just before stitching is started so that when lock stitches or bar stitches are formed at an end of a button 'nole slit, the button hole will be not stitched as it is widely open.

Heretofore, in the prior art mechanism, an upper cloth-presser body was provided with a pair of upper cloth pressers oppositely disposed on both sides against the stitching portion, the upper cloth-presser body moving up and down by a presser operating mecha nism. The upper cloth pressers which are adapted to be lowered by the operation of the presser operating mechanism and pressed from the upper side by a pressing spring at both sides of the stitching portion are connected to a starting mechanism of the sewing machine. A foot presser mechanism or treadle is manually operated to actuate the starting mechanism to start the operation of the machine and also to cause the upper cloth pressers to move toward one another to close the button hole and lock the pressers in their closed position. After the stitching is completed, the aforesaid lock is released by opening and raising the upper clothpressers by operating the presser operating mechanism. However, the prior art devices as mentioned above have inherent disadvantages in that much labor is required to manually operate the foot presser mechanism to move the upper cloth pressers and this manual labor for long hours tires operators which results in a decrease in the efficiency of the operation. Further, since the amount for drawing or condensing the work is constant, independent of the thickness of the cloth, in case of thick cloth the amount for closing the button hole is not sufficient to ensure that the end of the button hole will be stitched if it is widely opened or, on the contrary, in case of thin cloth the amount is excessive so that the end of the button hole will be stitched as it projects, which means the prior art devices have limited applicability.

SUMMARY OF THE INVENTION This invention eliminates the aforementioned disadvantages of the conventional sewing machine and provides a novel and improved cloth-presser mechanism in a sewing machine for bar or lock stitching a button hole at one end thereof by which the aforementioned disadvantage of the prior art mechanism are eliminated.

The principal object of this invention is to provide a novel work clamp mechanism which is constructed so that sufficient energy to move the depressed work clamps toward each other may be transferred from a drive force used by the main shaft of the sewing machine and accumulated in a spring element operatively combined in the mechanism during a cycle of the sewing operation. The thus accumulated energy is employed to close the button hole, thereby eliminating much hard manual labor which is required for operating the prior art mechanism.

According to one aspect of the present invention, there is provided a cloth-presser mechanism in a sewing machine for bar stitching a button-hole at one end thereof, which comprises a pair of work clamps carried by a work holder which is pivotally mounted on a vibrating plate which provides the vibratory movement required for the bar stitching, the work clamps being adapted to open and close in a horizontal plane and symmetrically with respect to the button hole slit line. A cam plate is movably mounted on the work holder and moves between two positions to control the opening and closing action of the work clamp. A rotary cam is interlocked with the main drive shaft of the sewing machine, and a control member is provided to receive a forward movement associated with the rotation of said rotary cam and a rearward movement regardless of said rotary cam. A first spring is disposed to accumulate energy due to the movement of said cam plate towards its one position, thus accumulated energy being employed to spread the work clamps, and a second spring is disposed to accumulate energy due to the for ward movement of said control member, thus accumulated energy from the second spring being employed to close the work clamps and move the cam plate towards its one position.

Other objects and advantages of this invention will further become apparent hereinafter and from the drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic side view of an over all embodiment of this invention showing a cloth-presser mechanism in a sewing machine;

FIG. 2 is a plan view of an embodiment of this invention partially showing a cloth-presser mechanism;

FIG. 3 is a sectional view taken along the line III III of FIG. 1-,

FIG. 4 is a sectional view taken along the line IV IV of FIG. 1',

FIG. 5 is also a sectional view taken along the line V V of FIG. 1;

FIG. 6 is a sectional view taken along the line VI VI of FIG. 2;

FIG. 7 is a sectional view taken along the line VII VII of FIG. 2;

FIG. 8 is a plan view ofa stitching portion in the sew ing machine as one embodiment and upper clothpresser showing their relationship;

FIG. 9 is a view ofa seam lockstitched in accordance with this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Although specific forms of the invention-have been i selected for illustration in the drawings, and the following description is drawn in specific terms for the purpose of describing these specific forms of the invention, this description is not intended to limit the scope of the invention, which is defined in the claims.

Referring now to the drawing, and particularly to FIG. 1, at the end of a main shaft (not shown) mounted in an overhanging arm 1 are a pulley 2 secured to the main shaft, and a pulley 3, which is not coupled to a load. A belt 4 is hung around pulley 3 and is transferred to the pulley 2 by means of a belt shifter 6 of a shut-off frame 5 which rotates around a shaft 103 through the action of a starting mechanism. After a seam cycle is completed the belt 4 is automatically shifted to the pulley 3 by means of the belt shifter 6 of the shut-off frame. Disposed on a bed 7, parallel thereto, is a vibrating plate 8 which is vibrated, as required for bar stitching, through a shaft 13 which is interlocked to a sewing mechanism (not shown) of the machine. An upper cloth-presser body or work holder 10 is pivotally mounted at one end on the vibrating plate 8 and the other end of the work holder oscillates in a vertical plane about a pivot 9. The other end of the vibrating plate 8 is provided with a lower cloth-presser or work supporting plate 12 on which the work is held. A pair of upper cloth-pressers or work clamps 11 and 11' for clamping the work to the plate 12 are carried by the work holder 10. The work clamps 11 and 11' have work clamp portions at the tip end thereof, which clamp portions are disposed at both sides of the button hole so as to press the upper surface of the cloth. The vibrating plate 8 is adapted to move back and forth along the upper surface of the bed 7 due to the movement of the shaft 13 so as to vibrate work clamps to bar or lock stitch the buttonhole at one end thereof in cloth which is positioned between the work clamps and the plate. Provided at the upper side of a standard 14 of the arm 1 is a cam 16 which is interlocked with the main shaft of the sewing machine and makes one revolution during each stitching cycle of the sewing machine and on which a slot is formed which is open at the periphery of the surface facing the standard. A holding plate 23 is fixed to the standard 14 by means of screws 24 at three projecting portions or lugs 17, 17 and 17". The lugs are integrally formed with the holding plate and serve to provide a gap 18 between holding plate 23 and the standard 14 as shown in FIGS. 3 and 4. The holding plate 23 is provided with four elongated slots 19, 20 (rectangular), 21 (FIG. 3) and 22 therein. Disposed in the gap 18, as shown in FIGS. 3 and 4, is a control member 28 having a projection 25 which extends outwardly from the upper right end of the control member and is adapted to engage the slot 15 of the cam 16 and an engaging portion 27 formed in the lower left hand portion of the control member 28. The control member 28 is connected to one end of a connecting rod 26, which extends through the elongated slot 22 and slides therein as shown in FIGS. 1 and 3. The control member 28 is movably secured to the holding plate 23 by means of a pin 29 which is slidably positioned within the slot 19 and a pin 30 which is smaller in diameter than the width of the rectangular slot 20 (FIGS. 1 and 4). The member 28 is forced leftwardly by means of a spring 31 which is connected to the standard 14 and the pin 30. The right hand portion of the control member 28, also moves upwardly. A pawl (or release) member 34 is also disposed within the gap 18, the pawl member 34 being pivotally mounted on a screw which is connected to the holding plate 23. The pawl member has an upward concave portion at its center which forms an inclined surface 32 that registers with the slot 21 of the holding plate 23, and a pawl surface 33 adapted to engage with the engaging portion 27 of the control member 28. The pawl member 34 rotates counterclockwise about the screw 35 by means of a spring 36 which is connected to the arm 1. As shown in FIGS. 1 and 3, a guide 39 is formed in the periphery of the hole 21 on the holding plate 23. A long slot 37 of the same size as the long slot 21 if formed on the guide 39 which is fixed to the holding plate 23 by means of screws 35 and 35' in such a manner that there is a gap between the holding plate 23 and the guide 39. A driving rod is provided and a bent portion 40 is rotatably connected to the lowermost end of a driving plate 44 and a bent portion 46 is inserted through the slots 21 and 37, and the plate 44 is pivotally connected to a bracket 42 by a pivot 43. The bracket 42 is mounted on the standard 14. The upper portion of the plate 44 is connected, through a link 41, to the shut-off frame 5. As shown in FIG. 3, the bent portion 46 of the driving rod 45 extends into the plane of the pawl member 34 and is formed with an inclined surface 47. A washer 48 is fixed to the bent portion 46 and a spring 49 is disposed between the washer 48 and the inside of the guide 39. The spring 49 forces the tip of the bent portion 46 to always project into the plane of the pawl member 34.

As shown in FIGS. 1 and 7, the upper cloth-presser body 10 is rotatably mounted on a bearing 51 which is attached to the vibrating plate 8 by the screw 50. On the flat upper portion 52 there are provided long slots 53, 54 and 55. Through the slot 53 projects a block 58 which is fixed to the end of a shaft 56 that is secured to the vibrating plate 8 and is provided thereon with a slot 57. As shown in FIGS. 2 and 6, a pin 63 extends through the slot 54, which pin 63 extends to the stopper 62 which has a lock portion 59 and is adapted to be fixed at any position on the surface of the flat portion 52 of the upper cloth-presser 10 by means of along slot 60 and a screw 61. As shown in FIGS. 2 and 7, a long slot 64 is formed in a connecting plate 68 and engages the right end of the connecting rod 26 at the upper surface of the upper cloth-presser body 10, and a connecting piece 67 (shown in FIG. 6) is integrally formed with the connecting plate 68. The connecting piece 67 has at its right portion, a connecting portion 65 for engaging the lock portion 59 of the stopper 62 and has at its left portion an inclined surface which forms pushing surface 66. The connecting plate 68 and a cam plate 70 are integrally connected by two stepped screws 71 and 71'. The cam plate 70 is formed with a pair of slots 69 and 69' which are, at its right hand portion, narrower inside and are, at the left hand portion, broader at its outside, respectively as shown in FIG. 5. The connecting plate 68 and cam plate 70 are integrally slidably movable within the slot 55. As shown in FIGS. 2, 6 and 7, a release member 74 is pivotally mounted by a pivot 73 on a support 72 which is secured to the upper clothpresser body 10 at the upper surface thereof. The release member 74 is provided with a pawl 75 which is disposed in the same direction as the connecting piece 67 of the connecting plate 68. A bent portion 102 of the member 74 extends into the slot 57 of the nose 58 together with a spring 76 which is provided around the shaft 73 and connected to the member 74 so as to force the member 74 to rotate in a clockwise direction. In FIG. 6, when the connecting piece 67 moves toward the left, the pawl 75 is pushed upwards by the pushing surface 66 and the connecting piece 67 moves to the chain line position. Once the piece 67 passes the pawl 75, the pawl 75 prevents the piece 67 from returning to its original position by engaging the right hand end of the connecting piece 67 at the position as indicated by the chain line.

As shown in FIGS. 1 and 5, below the right hand portion of the flat portion 52 of the upper cloth-presser body 10 the pair of upper cloth-presser 11 and 11' are rotatably positioned by stepped screws 77 and 77'. Pins 78 and 78', fixed thereto, extend into the slots 69 and 69, respectively, of the cam plate 70 and together with the right hand portions of the upper cloth-presser 11 and 11' are bent downwards so that the lower surfaces thereof are disposed at both sides of the end of the button hole along with the hole line thereof formed on the cloth. Therefore, since the pins 78 and 78' are moved inwardly by means of the slots 69 and 69 when the cam plate 70 moves leftwards as shown in FIG. 5, the free ends of the upper cloth-pressers 11 and 11' are moved toward each other. Further, as shown in FIGS. 2 and 7, above the right hand portion of the flat portion 52 of the upper cloth-presser body 10, a pressing member 84 is fixed by means of a screw 85. The member 84 is integrally formed with a pressing piece 80 which is bent upwardly and is also formed with recess 79 on the upper surface thereof. Pressing pieces 81 has two upwardly bent right sides. A guide piece 83 is bent downwards and so formed that the lower end of the piece 83 approaches the work and receives a thin guide plate 82. As shown in FIG. 7, the recess of the pressing piece 80 receives the lowermost end of a bar 89 which extends upwardly through a hole 88 of a supporting plate 87 which is provided under a projecting portion of the hollow arm 1. The bar 89 is forced downwards by means of a spring 91 provided between a screw 90 threaded on the bar 89 and supporting plate 87. The connecting plate 68 is biased by means of a spring 94 connected between a pin 92 provided on the upper surface of the pressing piece 81 and a pin 93 provided on the connecting plate 68. As shown in FIGS. 1 and 7, under the pressing piece 81 is disposed a pressing member 96 at the lowermost end of pressing bar 95.

As shown in FIG. 1, the pressing bar 95 is engaged with and extends within the projecting portion 86, and at the uppermost end of the bar 95 pressing plate 98 is secured thereto which plate 98 projects outwards from a hole 97. Below a pin 99, provided on the uppermost end of the plate 98, the right end of the pressing lever 101 is rotatably provided and pivots around a stepped screw 100 at the side of the hollow arm 1. The leftmost end of the pressing lever 101 (not shown) is adapted to be lowered through chains 104 by the operation of foot pressing.

The construction of the present invention is as aforementioned. The full lines in respective drawings designate the stop condition of the sewing machine in which the cloth 105 formed with the button hole slit is inserted between the work clamps 11, 11 and the work supporting plate 12 so that the end of the button hole is situated perpendicularly to the elongated opening defined by the ends of the work clamps, and the pressing lever 101 and chain 104 are released. In this state, the belt 4 is hung on the pulley 3 by means of the belt shifter 6 of the shutoff frame 5, the upper cloth-presser body 10 presses the cloth 105 on the surface of the lower work supporting plate 12 by means ofa spring 91 pressing the upper right end thereof with the upper clamps 11 and 11 spreading the button hole, as shown by the full line in FIG. 5. The lock portion 27 of the control member 28 is locked by the pawl 33 in the position as shown in FIG. 1.

When the starting mechanism (not shown) is operated, the shut-off frame 5 rotates counterclockwise around the shaft 103 which causes the main shaft of the sewing machine to rotate so that the machine starts and the cam 16 rotates in a counterclockwise direction. In accordance with the movement of the shut-off frame, the drive plate 44 rotates counterclockwise through the link 41 about the shaft 43, and the bent portion 46 of the lower driving rod 45 moves rightwards within the long slit 19 of the holding plate 23 and long slit 37 of the guide 39 so that it reaches the chain line position illustrated in FIG. 3. During this activity the end of the ben portion 46 pushes the inclined surface 32 of the pawl member 34 so that it rotates clockwise about the screw 35 against the spring 36 to disengage the pawl 33 from the lock portion 27 of the member 28. The pins 29 and 30 of the control member 29 move toward the left within the long slits 19 and 20, of the holding plate 23 by means of the spring 31 together with the connecting portion 25 of the member 28 which is formed towards the periphery of the cam 16 by means of the upward tension force of the spring 31. Thus, the control member 28 moves rearwardly independent of the direction of rotation of the cam 16. As the member 28 moves leftwards, the right hand portion thereof moves slightly downwards as it swings about the pin 29, and the pawl member 34 (previously rotated clockwise) returns to its original position by means of the spring 36. Further, by the rearward movement of the member 28 the connecting rod 26 engaging the member 28 moves leftwards to the chain line position as shown in FIG. 3. Since the connecting plate 68 is moved against the spring 94 the connecting rod 26, which extends into the slit 64 moves and the stepped screws 71 and 71 slide leftwards within the slit 55 of the flat portion 52 simul taneously with the cam plate as shown in FIG. 5 by the chain line. Thus, the work clamps l1 and 11' rotate about their pivots 77 and 77', respectively, through the movement of the pins 78 and 78 following the slots 69 and 69 with the ends of the work clamps moving toward each other as shown in FIG. 5 and 8 by the chain line, whereby the cloth 105 of the button hole end is drawn towards the linear line portion of the button hole to close up the button hole. Further, when the connecting plate 68 and cam plate 70 move leftwards from the position shown by the solid line, the pushing surface 66 of the connecting piece 67 of the connecting plate 68 pushes upwards the pawl of the release member 74 upwards against the springs 76 as shown in FIG. 6 by the chain line. When the connecting piece 67 moves toward the left hand portion of the pawl 75 as shown by the chain line (FIG. 6), the release member 74 re turns (as shown by the full line) by the operation of the spring 76 so that the connecting portion 65 is locked by means of the pawl 75. This locking position enables the cam plate 70 to move to the position shown in FIG. 5 by the chain line, whereby the cloth on both sides of the stitching portion moves inwards against the stitching portion by means of the work clamps l1 and 11, and the spring 94 accumulates energy which will be used to spread the work clamps.

In the aforesaid state, the button hole end will be lockswitched or barstitched as shown in FIG. 9, and in one detailed cycle of the seam forming process when the connecting portion 25 of the member 28 corresponds to the slot 15 of the cam 16 (rotating counterclockwise) since the portion 25 of the force accumulating plate 28 has been pushed to the outer periphery of the cam 16 by the operation of the first spring 31 to the position shown in FIG. 1 by the chain line, the connecting portion 25 enters the slot 15 so that as the counterclockwise rotation of the cam 16 proceeds, the member 28 follows the rotation of the cam 16 and moves rightwards against the spring 31 with the pins 29 and 30 guided in the long slits l9 and 20 and the connecting portion 27 pushing down the pawl 33 through the back portion thereof. Due to the above rightwards or forward movement of the member 28 the spring 31 accu' mulates energy which is used to close the work clamps. When the locking portion 27 finishes its rightward movement, the pawl 33 is pushed down and returns to its original position by means of the spring 36. Thereafter, the connection between the connection portion 25 of the member 28 (moving rightwards) and the slot 15 of the cam 16 will become disengaged, and the member 28 is pulled by the operation of the spring 31. However, since the connecting portion 27 engages the pawl 33, the member 28 is locked at the position shown in FIG. 1 by the full line. During the rightward movement of the member 28, the connecting rod 26 also moves rightwards. However, the right end thereof only moves within the long slit 64 of the connecting plate 68 as shown in FIG. 2 by the chain line so that the connecting plate 68 does not receive the force of the rightward movement, and the connecting pieces 67 thereof is locked at the position shown in FIG. 6 by the chain line.

When one cycle of the lockstitching process is finished so that the lockstitched seam is formed on the button hole end as shown in FIG. 9, the shut-off frame automatically rotates clockwise about the shaft 103 and the sewing machine is stopped by transferring the belt 4 to the pulley 3 by means of the belt shifter 6 as shown in FIG. 1 by the full line. By the clockwise rotation of the shutoff frame 5 the drive plate 44 rotates clockwise through the link 41 about the shaft 43. The bent portion 46 of the drive rod 45 moves rightwards in the long slit 19 of the holding plate 23 and long slit 37 of the guide 39 from the chain line position to the full line position as shown in FIG. 3. In the event the inclined surface 47 of the bent portion 46 strikes the member 34, the bent portion 46 compresses the spring 49, and moves to the full line position sa shown in FIGS. 1 and 3. In order to remove the cloth 105 from between the work clamps 11, 11' and the lower work supporting plate 12, the chain 104 of the pressing lever 101 (shown in FIG. 1) is pulled down by means of the foot pressing mechanism. The right end of the pressing lever 101 is raised and the pin 99 of the pressing plate 98 fixed to the pressing bar 95 is also raised. Since the pressing member 96 of the lower end of the pressing bar 95 lifts the pressing piece 81 of the pressing body 84 against the spring 91, the work holder will swing up about the pivot 9 as shown in FIG. 7 by the chain line to release the work clamps 11, 11' from the cloth 105 on the work supporting plate 12.

Furthermore, when the right hand portion of the upper clothpressing body 10 reaches the chain line position as shown in FIG. 7, the pivot 73 of the release member 74 is also raised. Since the bent portion 102 of the left portion of the member 74 is engaged in the slot 57 of the block 58 which is secured to the vibrating plate 8 through the stud 56, the release member 74 rotates counterclockwise about the pivot 73 against the spring 76 to the chain line position shown in FIGS. 6 and 7 and causes the pawl 75 to release the lock 58 with the connecting portion 65 of the connecting plate 68 at the chain line position as shown in FIG. 6. Then, the connecting plate 68 (locked in the chain line position as shown in FIG. 6) moves to the full line position shown in FIGS. 2 and 6, together with the lower cam plate 70, under the action of the tension of the spring 94, until the connecting portion 65 of the connecting plate 68 strikes the engaging portion 59 of the stopper 62. Also, by this movement, the campplate as shown in FIG. 5 moves rightwards from the chain line position to the full line position. Since the pins 78 and 78' are moved outwardly by the slots 69 and 69' the pressers 11 and 11' rotate about their pivots 77 and 77' so that the tips thereof open outwardly against the button hole as shown.

Furthermore, in order to stitch the next button hole end, the button hole formed on the cloth 105 formed with the button hole slit is disposed on the upper surface of the work supporting plate 12 as shown in FIG. 8. When the chain 104 which pulls pressing lever 101, is released by the foot pressing mechanism, the upper cloth-pressing body 10 is lowered by means of the bar 89, pressing body 84 and the spring 91. The tip of the work clamps l1 and 11' are disposed on the upper surface of the cloth with the tips thereof spread as shown. The member 74 moves to the position shown in FIGS. 6 and 7 by the chain line, and in the opposite direction when raising the upper pressing body 10. The pressing body is also lowered by lowering the pressing piece 81 of the pressing body 84 so that the pressing lever 101 rotates clockwise about the stepped screw through the pressing bar 95, pressing plate 98 and pin By the aorementioned steps the preparation of the lockstitiching of the next button hole end is completed, and each member is placed in the position as shown by the solid line, and by repeating the aforementioned operation the lock-stitching may be done in a state where the button hole end is almost closed.

Further, when the connecting plate 68 moves rightwards by means of the spring 94, the stopper 62, which locks the connecting portion 65 of the connecting piece 67 is slidably secured parallel to the direction of motion of the connecting plate 68. When the screw 61 is turned counter-clockwise to loosen it and to move the stopper 62 leftwards, since the screw 61 extends within the long slot 60 and the pin 63 is engaged within the hole 54 of the flat portion 52 of the upper clothpresser 10, the stopper 62 is tightened sliding it to the desired position by means of the screw 61. Thereby, the locking portion 59 of the stopper 62 moves more leftwards to be secured than its position as shown in FIG. 6. Since the connecting plate 68 moves rightwards from the chain line position by the operation of the spring 94, the cam plate 70 as shown in FIG. 5 does not move to the full line position as shown and it will be locked more leftward than the aforesaid position. Therefore, the moving distance of the slots 69 and 69' of the cam plate 70 for displacing the pins 78 and 79' is short so that the amount which the work clamps 11 and 11' open and close, namely the amount for drawing the work or closing up the button hole is decreased. Thus, the proper amount for drawing the work is obtained in response to the thickness of the cloth by selecting the position of the stopper 62 as desired.

As aforementioned, for moving the work clamps toward each other to close the button hole end of the cloth, the present invention does not require the strenuous work involved in operating the foot pressing mechanism of conventional mechanisms so that only the effort to release the energy of the spring accumulated in the operation of the sewing machine is needed. The operator does not become tired during long operation of the machine, and this results in improved efficiency of the operation. Since the amount for drawing the cloth by the upper cloth-presser may be selected as desired, the proper amount suitable for the kinds of the cloth may be obtained. Therefore, good results will always be obtained with the subject invention.

l claim:

1. A work clamp mechanism for use in a sewing machine having a bed for bar stitching a button-hole at an end thereof, comprising:

a vibrating plate (8) positioned on the bed (7) of the sewing machine and adapted to vibrate as required for bar stitching;

a work holder pivotally mounted on said vibrating plate (8) by a horizontally disposed pivot axis a pair of work clamps (11, 11') having clamp portions at the ends thereof and base portions pivotally supported on said work holder 10), the clamp portions adapted to reciprocatively move and being symmetrically positioned with respect to a button hole slit line;

a cam plate (70) adapted to control the movement of said work clamps and movably mounted on said work holder for movement between a first position for opening said clamp portions, and a second position for closing said clamp portions;

a first release member (74) operatively positioned to normally anchor said cam plate (70) in its second position and to release the cam plate from its second position when said work holder pivots upwardly from said vibrating plate;

a first spring (94) operatively disposed to accumulate energy produced by the movement of said cam plate towards its second position and to cause said cam plate to shift from its second position to its first position by means of the accumulated energy, in connection with the release of said cam plate by said first release-member (74);

a rotary cam (16) interlocked with a main drive shaft of the sewing machine;

a control member (28) disposed on a side of an arm (1) of the sewing machine and adapted to move forwardly in assoication with the rotation of said rotary cam (16) and to move rearwardly independently of said rotary cam;

a second release member (34) operatively positioned to anchor said control member (28) in its forward position and to release the anchored control member as the sewing machine is started;

a second spring (31 operatively disposed to accumulate energy due to the forward movement of said control member and to permit said control member (28) to move rearwardly due'to the accumulated energy developed in connection with the release of said second release member (34); and

means (26) connecting said control member (28) to said cam plate (70) for moving said cam plate towards its second position in accordance with the rearward movement of said control member (28). 

1. A work clamp mechanism for use in a sewing machine having a bed for bar stitching a button-hole at an end thereof, comprising: a vibrating plate (8) positioned on the bed (7) of the sewing machine and adapted to vibrate as required for bar stitching; a work holder (10) pivotally mounted on said vibrating plate (8) by a horizontally disposed pivot axis (9); a pair of work clamps (11, 11'') having clamp portions at the ends thereof and base portions pivotally supported on said work holder (10), the clamp portions adapted to reciprocatively move and being symmetrically positioned with respect to a button hole slit line; a cam plate (70) adapted to control the movement of said work clamps and movably mounted on said work holder for movement between a first position for opening said clamp portions, and a second position for closing said clamp portions; a first release member (74) operatively positioned to normally anchor said cam plate (70) in its second position and to release the cam plate from its second position when said work holder pivots upwardly from said vibrating plate; a first spring (94) operatively disposed to accumulate energy produced by the movement of said cam plate towards its second position and to cause said cam plate to shift from its second position to its first position by means of the accumulated energy, in connection with the release of said cam plate (70) by said first release-member (74); a rotary cam (16) interlocked with a main drive shaft of the sewing machine; a control member (28) disposed on a side of an arm (1) of the sewing machine and adapted to move forwardly in assoication with the rotation of said rotary cam (16) and to move rearwardly independently of said rotary cam; a second release member (34) operatively positioned to anchor said control member (28) in its forward position and to release the anchored control member as the sewing machine is started; a second spring (31) operatively disposed to accumulate energy due to the forward movement of said control member and to permit said control member (28) to move rearwardly due to the accumulated energy developed in connection with the release of said second release member (34); and means (26) connecting said control member (28) to said cam plate (70) for moving said cam plate towards its second position in accordance with the rearward movement of said control Member (28). 